On 26 November 2009, Krychowiak joined Championnat National side Stade de Reims on loan until the end of the season.[4] He quickly became a regular in the starting eleven and scored two goals to help the club win promotion to Ligue 2. Reims and Bordeaux agreed to extend the loan for another season. Krychowiak was a regular starter as the club finished 10th in its return to Ligue 2 and was voted by fans as the team's player of the season.[5] Although Krychowiak usually plays as a defensive midfielder, on rare occasions he has also appeared in central defense. On 17 November 2011 he joined Nantes on loan until the end of the season.[6]

In June 2012, Krychowiak signed a three-year contract with Stade de Reims, which was newly promoted to Ligue 1.[7]

On 30 August 2017, it was announced that Krychowiak had joined Premier League club West Bromwich Albion on a season-long loan.[14] On 14 October while on loan at West Bromwich Albion, Krychowiak said to the media that he felt deceived by Paris Saint-Germain manager Unai Emery saying "I spoke with the coach but every time when I spoke with him I felt deception". He went on to say "Yes, exactly. So for me I didn’t understand why. The coach knows me very well. We spent two years together and before I signed the contract he told me to come to PSG, and I didn’t play." This was in response as to his frustration of being left out of the team and not getting game time.[15][16][17]

Krychowiak represented Poland under-20s at the 2007 FIFA U-20 World Cup and scored a free kick against Brazil, the only goal of the match. He was the youngest outfield player named to the Polish U20 squad. He made his first appearance for the senior Polish national team in a friendly against Serbia on 14 December 2008. Since the game was not on an official FIFA date, the teams were mostly composed of players from the domestic leagues, as well as a few reserve players, however, it was counted as an official match.[19][20]

On 14 November 2014, Krychowiak scored his first international goal, Poland's second in a 4–0 UEFA Euro 2016 qualifying win in Georgia.[21] His second goal came in Poland's final qualifying match against Ireland, where he opened the scoring in a 2–1 victory which made Poland qualify for Euro 2016.
In Poland's opening game against Northern Ireland, he was voted man of the match. This was Poland's first ever win at a European Championship. He scored the final spot kick in a 5–4 penalty shootout win over Switzerland in the round of 16. He played every minute of Poland's historic Euro 2016 campaign, which ended in the quarter-finals losing to Portugal 3–5 in a penalty shootout.